Previous studies have shown that patients admitted to the intensive care unit (ICU) after "office hours" are more likely to
die. However these results have been challenged by numerous other studies. We therefore analysed this possible relationship
between ICU admission time and in-hospital mortality in The Netherlands. This article relates time of ICU admission to hospital
mortality for all patients who were included in the Dutch national ICU registry (National Intensive Care Evaluation, NICE)
from 2002 to 2008. We defined office hours as 08:00-22:00 hours during weekdays and 09:00-18:00 hours during weekend days.
The weekend was defined as from Saturday 00:00 hours until Sunday 24:00 hours. We corrected hospital mortality for illness
severity at admission using Acute Physiology and Chronic Health Evaluation II (APACHE II) score, reason for admission, admission
type, age and gender. A total of 149,894 patients were included in this analysis. The relative risk (RR) for mortality outside
office hours was 1.059 (1.031-1.088). Mortality varied with time but was consistently higher than expected during "off hours"
and lower during office hours. There was no significant difference in mortality between different weekdays of Monday to Thursday,
but mortality increased slightly on Friday (RR 1.046; 1.001-1.092). During the weekend the RR was 1.103 (1.071-1.136) in comparison
with the rest of the week. Hospital mortality in The Netherlands appears to be increased outside office hours and during the
weekends, even when corrected for illness severity at admission. However, incomplete adjustment for certain confounders might
still play an important role. Further research is needed to fully explain this difference

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